Why did the repair dept. remove and not return the SIM card in my iPhone?

Typically, if you don't get your SIM back, when iPhones either get sent to Apple from an Apple Authorized Service Provider or when Apple takes them to their repair department, the SIM tray wasn't checked.

If the phone goes to a repair facility, typically in California, the people who repair the devices don't even look. I would contact the place you took your device and see if it's still there. It is possible that it was just overlooked and not installed back into the iPhone after it was repaired/replaced.

Unfortunately, it is not an abnormal issue. Contact your local cell carrier (whoever your provider is), and quite often, they will replace your SIM at no charge.

Good luck!

Call Apple back and ask them. It may have simply been an honest oversight or mistake on their part.

You would have to ask them. This is a user to user forum only, no way for us to know.

Don't waste time trying to track down the old SIM. Just get a new one from your carrier.

You were told before you sent the phone in for repair to remove the SIM card. Get a new one from your carrier.